Transparent protective shield



A. G. abn-:TZ ETAL 2,861,021

TRANSPARENT PROTECTIVE SHIELD Nov. '18, 195s Filed Dec. 1s, 195e UME/DEINVENTOR: Amena G. HDietg lfwed E Moonen] ATTORNEY United tates Patent UTRANSPARENT PRTECTIVE SHIELD i Albert G. H. Dietz, Winchester, and FredE. Mooney,

Harvard, Mass., assignors to the United States of America as representedby the Secretary of the Army This application is a continuation-impartof our copending application Serial Number 2,146, filed January 14, 1948(now abandoned).

Our invention relates to transparent shatterproof sheet materialemployed to protect personnel from flying splinters and fragments,particularly for use in eye armor.

`Although materials have been developed with generally satisfactoryresults for such uses as automobile windshields and windows, there is-no material known to us which has hitherto proved satisfactory for usein military vehicles, aircraft, or ships where shrapnel and highvelocity projectiles are encountered. We do not principally propose amaterial of armored character, resistant to the passage of theprojectiles themselves but are concerned rather mainly with protectionagainst shrapnel as well as the elimination of the flying splinters and`fragments ordinarily incident to the passage of the projectile through atransparent window.

We have discovered that a highly successful transparent splinter-proofshield may be constructed of laminated plastic layers of differingcharacteristics.

Briefly speaking our invention comprises a plurality of laminations oftransparent material bonded together to produce an integral sheet inwhich one or more of the laminations are relatively hard and thereforerelatively frangible, while other layers, particularly the inside layer,are composed of relatively tough resilient material. When a mass strikesthe outside of the sheet, the hard layers may crack and shatter but indoing so distribute the impact over a relatively wide area so that theimpact force per unit area is substantially reduced. On the other hand,the resilient material absorbs the force by converting it into kineticenergy dissipated by the Work done to return the material to normalposition. In such a sheet it is essential that there be a layer of theresilient material interposed between the person or area to be protectedand theinnermost layer of the hard frangible material.

The various features of our invention will be more readily understoodand appreciated from the following detailed description of twoembodiments thereof selected for purposes of illustration and shown byway of example in the accompanying drawing.

In the description which follows we employ the terms outside and insideand outer and inner as they would be used in connection with a window,port, or blister set in an airplane or ship.

In the drawing:

Fig. l is a perspective View of a preferred transparent protectivelaminated sheet in accordance with our invention;

Fig. 2 is an elevational front View `of the same sheet as it appearsafter the impact of a projectile such` as a small shell fragment;

Fig. 3 is a side elevation corresponding to Fig. 2;

Fig. 4 is a cross sectional view taken along lines 4 4 f Fig. 2;

2,861,021 Patented Nov. 18, 1958 Fig. 5 is a perspective view ofanother, but less prel ferred form of our invention; and i Fig. 6 is aperspective view of a goggle embodying a transparentprojectile-penctration-resistant sheet in accordance with our invention.

As shown in Fig. 1 of the drawing, we form, in the preferred form of ourinvention, a projectileand projectile-fragment-penetration-resistantnon-splintering transparent shield, composed of al thick, rigid,shatterable transparent outer layer of polymethyl methacrylate, amaterial which is relatively hard and frangibleg; a tough flexible,non-shatterable resistant transparent thin intermediate layer ofpolyvinyl butyral bonded to the inner surface of the outer polymethylmethacrylate layer, and a very thin high-tensile-strength elongatabletransparent innermost layer bonded to the inner surface of theintermediate polyvinyl butyral layer. The outermost first layer 1t) ofpolymethyl methacrylate may be composed of one or more (e. g., two)plies but we presently prefer it to be a single ply as shown in Fig. 1.The intermediate layer 11 of polyvinyl butyral is likewise composed ofone or more plies, whose total or aggregate thickness is substantiallyless than the thickness of outer layer 10; in view of present-daydifficulties in securing polyvinyl butyral films of adequate thicknessto possess `the necessary ballistic properties, we presently prefer toemploy a plurality, say about tive to seven plies of polyvinyl butyralfilm laminated to each other to constitute such intermediate layer. Theinnermost layer 12 is (preferably) a single ply of a transparenthigh-tensile-strength elongatable plastic substance, Vsuch as polyamidefilm (nylon), polyester film (e. g., polyethylene terephthalate, asubstance sold by E, I. duPont de Nemours & Co. under the trademarkMylar), or a regenerated cellulose sheet. The several laminations arebonded together to form anintegral sheet, preferably by fusing theplastic layers together under elevated temperatures. Alternativelycement may be employed to form the bond, but fusing is preferable. Thematerial may be produced in fiat sheets capable of being cut to suitableshapes or the material may be assembled in a mold to form integralcurved pieces as fo-r curved lens goggles, aircraft blisters, noses,etc. Conventio-nal molding techniques have been found satisfactory. t

in a less preferred embodiment of our invention shown in Fig. 5, theoutermost or iirst layer 13 is composed of polymethyl methacrylate; thenext or second layer 14 of polyvinyl butyral; the third layer 15 ofpolymethyl methacrylate; the fourth layer 16 of polyvinyl butyral; thefifth layer V17 of polymethyl methacrylate; the sixth layer 18 ofpolyvinyl butyral; and the innermost layer 19 of a polyamide (nylon),polyester (e. g., Mylar) film or a regenerated cellulose sheet.

A clearer understanding of the invention will be promoted by referenceto the action of our sheet in various contingencies, as compared to theaction of a Sheet of safety glass comprising a layer of relativelyflexible material sandwiched between two layers of hard frangiblematerial. p

If an expanse of a sheet constructed as shown in the drawing is struckby a high velocity projectile such,for example, as a 50 caliber machinegun bullet, the bullet will pass completely through the sheet leavingbehind it a through-and-through aperture all of the walls of which arerelatively even. Although the outer layer 10 may crack into fragments,the innermost layer 12 will exhibit only a round hole and no fragments,splinters, or spalls will be ejected from the sheet on the insidethereof. In the case of ordinary safety glass, there is extremelikelihood that the innermost layer will shiver andV that splinters ofglass will tiy from the sheet.

ice

of outer layerl', and thus distribute and dissipate the aviators goggle20, `having a protective face vp'ieceJZl o! erably multi-ply) layer ofpolyvinyl butyral of an aggre- 45 at least about .05 in. and beingthinner 'thansaid Cuit? gate thickness of about .05 to .12 in., and a(preferably layer, and a thinV high-tensile-strengthVelongatable,trzpmgM 2,861,021 r s 4 f 'If the outermost surface of thesheet shown in the individual layer being preferably composed of fromabout drawing be struck by a relatively large object as by a ve to sevenplies of an individual thickness 'of 'about direct shell hit at lowvelocity or by a glancing blow at .015 in. each. The innermost layer 19of nylon, polyester high velocity, the` outermost layer k will becracked and or regenerated cellulose may likewise have a thickness ofbrokennto'fragments over a considerable area, as illus- 5 .00311002 in.as in the principal embodiment. trated Ain Fig. V2,; however, the'laminated intermediate principle of operation of the embodiment of Fig.5 is polyvinyl butyral layer Y11 will yield to the blow and stantiallyanalogous to the principal embodiment of embed the projectile orprojectile-fragment P, whose 1-4, except that the splintering of,successive polymethyl' energy has already been dissipated 'in part byits contact methacrylate layers 13, 15, and 17 will be progressively:with outer layer'10. Some of the plies of the interme- 10 less uponimpact by a projectile .or projectileffragmj, diate Vlayer '11 mayor maynot be disrupted depending The protective ballistic limitof theYembodlments of Fi'gfSj upon the force of the impact. However, thedisrupted is substantially the same as the embodiment of Figs. 1 i asWell as the undisrupted plies -of Vintermediate layer 11 however, itsuffers from the disadvantage that it is will also serve 4toembed anysplinters (as shown in Fig.l 4) cut to curve, as on curving of thelaminated sheet, tha fro'mthe shattered area of outer layer l0. and thusprevent 15 Ypolyvinyl butyial'layers 14,116 and 18 tend to creep,,thein'from coming into contact with the faceof the wearer, consequentlack of uniformity in the aggregate thickness` where otherwise it mighthave inflicted an eye injury of a of the polyvinyl butyral layers, whichreduces the uniform severitycomparable'to theinjury-of that which wouldhave protective qualities of the kcurved eye shield. '2 been inflictedby the shell fragment, if no eye-protective As shown in Fig. 6 ofthedrawing,var Vprotective device v'had been worn. The impact stress uponinter- 20 shield in accordance with our invention may "belincdr mediatelayer `11 will be in excess ofthe shattered area porated, e. g., in aconventional goggle resembling fm.

residual forward momentum of the projectile-fragment. spongerubber oranalogous material in order to soften@ 0The tough elongatable innermostlayer 12 serves to back thrust exerted by a projectile orprojectile-fragment wlmi -up Ythe intermediate layer 11 and vto confinethe inward 25 it strikesthe eye shield 22. As shown in Fig. 6, eye shi fb ulge (see Fig. 3) created by the impact of the fragment 22 ispreferably slightly curved for -better vision;l

to a lmoderate depth so as to `avoid a blow against the a desirable, butnot an indispensable feature of ourjflk face of the wearer. Theinnermost layer 12 also serves vention. the subsidiary `purpose ofprotecting the device against "While changes in the arrangement,proportions, dirx'lhg scratches and embedding of dust and other foreignparsions and shape of the `protective eye shield and ticles,whichlotherwise would tend to accumulate on the ponent parts thereof,disclosed'in this specification 'r inside ofthe shield because of thesomewhat tacky nature readily occurs to the expert without departingfrom of polyvinyl butyral, especially in a hot climate. spirit ofthe'invention, it is our desire lto encompass sua! i" e Asis the caseinall items of body armor, an effective variations within the scope ofsuch invention; we 'thfg compromise-must be'struck in the eye arrnor ofthe pres- 35 desire to be limited only by the appended claims. entinvention between thickness `and ballistic protection. We claim: Inother words, a very thick shield though possessed of 1. A projectileandprojectileffragment-penetrationrejf great protective capacity, wouldrender the goggle in sistant non-splintering transparent shield, comprisingt which it -isfincorporated so heavy that the wearer will notthick, rigid, shatterable transparent outer layer of po be able'to useit eifectively in combat. We have found 40 methyl methacrylate, saidouter layer having a t-hckncnaA4 that aprotective eye armor shield inaccordance with the from about .25 to about .5 in., a tough, ilexible,nog; above-explained principles of our invention, may be comshatterableresilient transparent thin intermediate 'lay' gg posed of an outer layerof polymethyl methacrylate havof polyvinyl butyral bonded to the innersurface Vof ing a thickness of about .3-.5 in., an intermediate(prefouter layer, said intermediate layer ,having a thickness/!single-ply) `innermost layer of nylon, polyester or regenparent innerlayer bonded to the Ainner surface of said erated cellulose ilm of athickness from about .001 to intermediate layer, said inner-layer beingof 'a 'thicknel` "L about .0l in. In the actual Yembodiments illustratedin of at least about .1001 in. and 'having lesser thickness `1 Figs.I1*-4, -the outer polymethyl methacrylate single-ply 50 a'harder surfacethan said polyvinylbutyralintermediatn layer hasa'thickness of .375i.045 in. (the variation being layer, and said vinner'layervbeinga'mem'ber of the fgi'oult` due tothe manufacturers factorytolerance), the tive consisting of polyamide, Apolyester andyregenerated.cellula'Y p'liesof the vintermediate polyvinyl butyrallayer have an lose; whereby when said outer layer is shattered `by*aggregate thickness of about .075 i.015 in. (correspondprojectile orprojectile-fragment,'the sp'linters'of said outer ing to anaveragethickness of .015i.003 in. for each inlayer are embedded in rsaidintermediate layer backed dividual ply), and the innermost layer 14 hasa thickness said inner layer, and said projectile or projectile-fragmentof about .003i.002 in. This sheet was found to have a is stopped beforepenetrating `said inner layer. l .f protective glimit of 1510 ft./ sec.,i. e., was capable of stop- 2. A projectileandprojectilefragment-penetratoi) ping 50% ofthe vfragments delivered by a17-grain fragresistant non-splintering 'transparent shield, comprisil,rn-entationbullet traveling 1510 ft./sec. at the instant of a thick,rigid, shatterable transparent outer layer ofpoly impact. The protectionis comparable to the protection methyl methacrylate, said outer vlayerhaving a tliick'ves'` alforded by thestandard Army Armored Vest, and isfrom about .25 to about .5 in., a tough, flexible, nongr f presentlysuicient for combat conditions; e. g., against shatterable lresilienttransparent thin intermediatefla" most hand grenade, mortar andanti-aircraft shell fragof polyvinyl butyral bonded to the 'innervsurface of :sai

ments,mineffragments, and against pistol or subrnachineouter layer, saidintermediate layer having a tlickncsk gun bullets, although not against.30 cal. ritle bullets and 0f at least abOUt -05 inand being thnnef'llal,Sidf

machine-.gun bullets `unless ricochetting or nearly spentouter layer,and a thin high-tensile-strength elongatable -Inthelembodiment of ourinvention illustrated in Fig. TaHSPareDt inner Tegel'lefted Cellulose'layer Bonded @j 5.,-the 'individual layers of polymethyl methacrylate13, 1S the inner surface of said intermediate layer, said inner' and '17are of lesser thickness than that of the single-ply 7() layer being of athickness'of at least about .OOl'iin. and*A polymethyl methacrylatelayer of the embodiments 0f having Vlesser thickness and .a hardersurface than said Figs. :1-4 thereof, ;e.g of a thickness of about .25in. or polyvinyl butyral intermediate layer; :whereby nwhen' vsaitj lesseach. The intermediate layers of polyvinyl butyral n outer layer is`shattered by a projectile or `projectile-fragfV` 14, 16 ,and '1,8 varevof about `the same ythickness as in the ment, lthe vsplinters =of said'outer 4layer Yare embedded in principal embodiment, i; e about .0S-,.12in. each, each .Said intermediate layer backed by said inner layer;'and

said projectile or projectile-fragment is stopped before penetratingsaid inner layer.

A3. A projectileand projectile-fragment-penetrationresistantnon-splintering transparent shield, comprising a thick, rigid,shatterable transparent outer layer of polymethyl methacrylate, saidouter layer having a thickness from about .2S to about .5 in. a tough,exible, nonshatterable resilient transparent thin intermediate layer ofpolyvinyl butyral bonded to the inner surface of said outer layer, saidintermediate layer having a thickness of at least about .05 in. andbeing thinner than said outer layer, and 'a thin high-tensile-strengthelongatable transparent inner polyamide layer bonded to the innersurface of said intermediate layer, said inner layer being @of athickness of at least about .001 in. and having j lesser thickness and aharder surface than said polyvinyl `butyral intermediate layer; wherebywhen said outer layer is shattered by a projectile orprojectile-fragment,

the splinters of said outer layer are embedded in said i intermediatelayer backed by said inner layer, and said projectile orprojectile-fragment is stopped before penetrating said inner layer.

4. `A projectileand projectile-fragment-penetrationresistantnon-splintering transparent shield, comprising a thick, rigid,shatterable transparent outer layer of polymethyl methacrylate, saidouter layer having a thickness from about .25 to about .5 in. a tough,ilexible, nonshatterable resilient transparent thin intermediate layerof polyvinyl butyral bonded to the inner surface of`said outer layer,said intermediate layer having a thickness of at least about .05 in. andbeing thinner than said outer layer, and a thin high-tensile-strengthelongatable transparent inner polyester layer bonded to the innersurface of said intermediate layer, said inner layer being of athickness of at least about .001 in. and having a harder surface thansaid polyvinyl butyral, whereby when said outer layer is shattered by aprojectile or projectile-fragment, the splinters of said outer layer areembedded in said intermediate layer backed by said inner layer, and saidprojectile or projectile-fragment is stopped before penetrating saidinner layer.

5. A projectileand projectile-fragment-penetrationresistantnon-splintering transparent shield according to claim 1, wherein atleast one of said outer and intermediate layers consist of a pluralityof plies.

6.v A projectileand projectile-fragment-penetrationresistantnon-splintering transparent shield, comprising a thick, rigid,shatterable transparent outer layer of polymethyl methacrylate, saidouter layer being a single ply of a thickness from about .3 to about .5in., a tough, eXible, non-shatterable resilient transparent thinintermediate layer of polyvinyl butyral bonded to the inner surface ofsaid outer layer, said intermediate layer having a thickness of at leastabout .05 in., and being thinner than said outer layer and a thinhigh-tensile-strength elongatable transparent inner layer bonded to theinner surface of said intermediate layer, said inner layer being of athickness of at least about .001 in. and having lesser thickness and aharder surface than said polyvinyl butyral intermediate layer, and saidinner layer being a member of the group consisting of polyamide,polyester and regenerated cellulose; whereby when said outer layer isshattered by a projectile or projectile-fragment, the splinters of saidouter layer are embedded in said intermediate layer backed by said innerlayer, and said projectile or projectile-fragment is stopped beforepenetrating said inner layer.

7. A projectileand projectile-fragment-penetrationresistantnon-splintering transparent shield, according to claim 6, wherein saidintermediate layer of polyvinyl butyral consists of a plurality of plieswhose aggregate thickness is substantially less than the thickness ofsaid outer layer.

8. A projectileand projectile-fragrnent-penetrationresistantnon-splintering transparent shield according to claim 7, wherein thereare about live plies in said intermediate layer.

9.A A projectileand projectile-fragment-penetrationresistantnon-splintering transparent eye shield according to claim l, wherein thethickness of said outer layer of polymethyl methacrylate is from about.3 to about .5 in., the thickness of said intermediate layer ofpolyvinyl butyral is from about .05 to about .12 in., and the thicknessof said inner layer is from about .001 to about .0l in.

10. A projectileand projectile-fragment-penetrationresistantnon-splintering transparent eye shield according to claim 1, wherein thethickness of said outer layer of polymethyl methacrylate is about.3751.045 in., the thickness of said intermediate layer of polyvinylbutyral is about .075 i015 in., and the thickness of` said inner layeris about .0031.002 in.

l1. A projectileand projectile-fragment-penetration resistantnon-splintering transparent shield comprising la plurality ofalternating laminated strata of thick, rigid, shatterable transparentlayers of polymethyl methacrylate, each of said polymethyl methacrylatelayers having a thickness of about .25 in., and tough, exible,nonshatterable resilient transparent thin layers of polyvinyl butyral,each of said polyvinyl butyral layers having a thickness from about .05to about .l2 in., and a thin high-tensile-strength elongatabletransparent innermost layer bonded to the inner surface of the lastpolyvinyl butyral layer, said innermost layer being of a thickness of atleast about .001 in. and having lesser thickness than and a hardersurface than any of said polyvinyl butyral layers, and said innermostlayer being a member of the-group consisting of polyamide, polyester andregenerated cellulose; whereby when said polymethyl methacrylate layersare shattered by a projectile or projectilefragment, the splinters ofsaid polymethyl methacrylate layers are embedded in said polyvinylbutyral layers, and said projectile or projectile-fragment is stoppedbefore penetrating said inner layer.

References Cited in the file of this patent UNITED STATES PATENTS2,387,227 Andersen et al Oct. 23, 1945 2,417,383 SwitzerA Mar. 11, 19472,417,837 Paggi Mar. 25, 1947 2,418,018 Ernsberger et al Mar. 25, 19472,456,467 Swedlow Dec. 14, 1948 2,464,826 Neher et al. Mar. 22, 1949

1. A PROJECTILE- AND PROJECTILE-FRAGMENT-PENETRATION-RESISTANTNON-SPLINTERING TRANSPARENT SHIELD, COMPRISING A THICK, RIGID,SHATTERABLE TRANSPARENT OUTER LAYER OF POLYMETHYL METHACRYLATE, SAIDOUTER LAYER HAVING A THICKNESS FROM ABOUT .25 TO ABOUT .5 IN., A TOUGH,FLEXIBLE, NONSHATTERABLE RESILIENT TRANSPARENT THIN INTERMEDIATE LAYEROF POLYVINYL BUTYRAL BONDED TO THE INNER SURFACE OF SAID OUTER LAYER,SAID INTERMEDIATE LAYER HAVING A THICKNESS OF AT LEAST ABOUT .05 IN. ANDBEING THINNER THAN SAID OUTER LAYER, AND A THIN HIGH-TENSILE-STRENGTHELONGATABLE TRANSPARENT INNER LAYER BONDED TO THE INNER SURFACE OF SAID